The present invention relates generally to optical scanners, and, ore specifically, to a dual aperture optical scanner.
U.S. Pat. No. 5,229,588--Detwiler et al discloses an exemplary dual aperture optical scanner for reading a bar code positioned on the surface of an article or item. A laser diode projects a laser beam against a polygon spinner having a plurality of mirrored facets which reflect the laser beam in sequence against various pattern mirrors for producing scan lines which project outwardly through horizontal and vertical apertures or windows. The pattern mirrors are arranged in sets of primary and secondary mirrors specifically oriented in space for generating specific scan lines. As the spinner rotates during operation, the scan beam traces the pattern mirrors in sequence for generating a finite number of scan lines. By mounting each facet of the spinner at a different elevation angle, corresponding, parallel sets of scan lines may be generated from the same sets of mirrors.
Each item has several sides and is typically in the form of a rectangular box having six sides including a front side facing the vertical window, an opposite back side, a bottom side facing the horizontal window, an opposite top side, and leading and trailing sides defined by the relative swiping of the item across the windows. A typical bar code includes a series of varying width alternating bars and spaces arranged in a conventional manner, such as a one-dimensional Uniform Product Code (UPC), for recording suitable data such as identity of the item to which it is attached. The bar code is printed on a label which may be mounted on any of the six sides of the item.
By using a dual aperture scanner, more sides of an item may be illuminated with scan lines for increasing the performance of the optical scanner for reading variously positioned bar codes irrespective of the sweeping orientation of the item past the windows. In this way, bar codes may be read with more accuracy and reliability over a greater range of item orientation in space to thereby increase throughput of the items being scanned.
A bar code may be positioned on the item in either a ladder orientation with the bars being spaced apart vertically on the item in a ladder fashion, or in a picket orientation with the bars being spaced apart horizontally in a picket fence fashion. In order to properly read a bar code, a scan line must traverse in sequence the alternating bars and spaces, and therefore ladder bar codes and picket bar codes require different orientation of the scan lines for effecting a successful read thereof.
In a practical configuration of dual aperture optical scanners, a finite number of pattern mirrors and spinner facets may be used to produce a finite number of scan lines which defines the total scan budget. The pattern mirrors are suitably configured and positioned in the limited volume of the scanner housing to produce scan lines of various orientation through the horizontal and vertical windows for reading ladder and picket bar codes over a preferred range of item orientation relative to the windows.
The pattern mirrors are therefore disposed to generate a first pattern of scan lines through the horizontal window, and a second pattern of scan lines through the vertical window which splits the scan budget for covering various sides of the item. The first scan pattern in the horizontal window is configured for scanning at least the bottom side of the item, and the second scan pattern through the vertical window is configured for scanning at least the front side of the item, with limited leading and trailing side coverage of the item also being provided by these two windows.
In U.S. Pat. No. 5,229,588 identified above, the vertical window provides a scan line pattern for scanning both ladder and picket bar codes from the front side of the item. It also provides scan lines for scanning ladder bar codes on the leading and trailing sides. And, the scan line pattern from the horizontal window is effective for scanning bar codes on the bottom side of the item. It also provides scan lines for scanning picket bar codes on the leading and trailing sides. However, this dual aperture scanner lacks the ability to scan the back side of the item, including ladder bar codes thereon.
Accordingly, it is desired to provide an enhanced dual aperture optical scanner effective for additionally scanning the back side of an item, with improved leading and trailing side coverage for ladder bar codes.